Automatic telephone system



H. P. CLAUSEN.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED MAY 24, 1918.

Patented July 8, 1919.

2 SHEETS-SHEET l OIIIIII.

H. P. CLAUSEN.

AUTOMATIC TELEPHUNE SYSTEM.

APPLICATION FILED MAY 24. 1918.

Patented July 8, 1919.

2 SHEETS-SHEET 2.

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HENRY P. CLAUSEN, OF MOUNT VERNON,

NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INGORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE SYSTEM.

Specication of Letters Patent.

Patented July 8, 1919.

Application led Hay 24, 1918. Serial No. 236,373.

To all 'whom'fit 'may concern:

Be it known'that I, HENRY P. CLAUSEN, a citizen of the United States, residing at MountJ Vernon, in the county of Westchester, State of New York, have invented certain new and useful Improvements in Automatic Tele hone Systems, of which the following is a ull, clear, concise, and exact description.

This invention relates to telephone systems emplo ing automatic switching appa- Y ratus for t e purpose of establishing conversational connections and particularly to Systems of this character having a capacity for a large number of subscribers lines.

In telephone systems comprising a plurality of central ofiioes and a comparatively large number of subscribers lines, in whic switching facilities are provided such that a subscriber may extend a connection from his own ofiice into any of the other oliices, and finally complete the connection to a desired line therein, it often becomes necessary for the subscriber in so extending his line to set up a long train of switch-ing mechanisms consisting of several selective switches. It may frequently happen that the calling party, in building up a connection of this character where a large number of digits is concerned, inadvertently manipulates his sender to transmit an improper digit after havin partly completed aconnection over a numier of the switches in the train. The result is that the particular switch which is being operated at the time the improper digit is sent is not set in operative relation to the desired group of trunks. It is, therefore, necessary that the falsely set switch be restored to its normal position before the call may be roceeded with, and it is moreover desirab e that such switch be restored to the exclusion of, and without affecting the preceding switches in the connection. This feature 18 of special advantage in large systems since it enables the calling party to retain, to the exclusion of other subscribers. the use of that portion of the train of switches successfully operated up to the point where the wrong digit is sent.V

Considering again telephone systems of the above mentioned character wherei a plurality of central offices are concerned, and wherein private branch exchanges are associated with the central offices, with switching facilities whereby any subscriber in the system ma obtain connection withA any other subscri er, it frequently occurs that a long train of switches must be employed in extending a connection to a subscribers line belonging to one of the private branch exchanges. This will necessarily be true where the calling line is individual to some office other than that with which the private branch exchange containing the called line is associated. In view of this necessity of setting up long trains of switches, and further in view of the fact that a calling subscriber, regardless of the office to which his line belongs, after having completed a conversation with one subscriber to a private branch exchange very often wishes to get in touch with another subscriber to the same exchange, it becomes desirable that he be able to release only that portion of the train of switches which is located in the private branch exchange, without disturbing the remaining switches. The set switches in his own and in all other central otlices preceding the called private branch exchange ma therefore be retained to his exclusive use while he proceeds in the usual manner to set other switches in the called exchange to obtain connection to other subscribersv lines.

In view of the foregoing, the present invention has as its eneral object the provision of a telep one exchange system equipped with means whereby a calling subscriber may, either during the process of extending a connection over a train of switches, or after having completed the connection toa called line, release a portion only of such train of switches, leaving undisturbed the preceding switches employed in, the extension of the connection.

A feature consists in the provision of means associatedwith one of the switches of a train of operated switches which is responsive only to a characteristic series of impulses sent from the calling substation to affect the electrical condition of the release trunk leading back to the next preceding switch in the train. This condition serves to bring about the restoration of such switch, which, however, in releasing does not cause the release of the remaining switches, but is adapted to'guard against the application of the releasing condition to the release trunk leading back therefrom.

lowing description.

In the'drawings accompanying this specication, Figure 1 shows a portion of a telephone system arranged in accordance with one embodiment of the invention. This figure illustrates subscribers lines and substations and selective switches for interconnecting the same, together with means `whereby any one of a train of selective switches may be operated in its primary movement by the calling subscriber at any point in the process of extendingr a connection to cause the release only of the next preceding set switch, while all other switches between the one released and the calling line remain intact in their operated positions. Fig. 2 is a showing in part of a telephone system involving another embodiment of this invention. This figure depicts a system havin subscribers lines with automatic switches or interconnecting the same, and also means associated with the final or connector switch employed in a completed oonnection which is responsive only to a characteristic series of impulses transmitted from the calling substation to .effect the release of the switch immediately preceding, to the exclusion of all other switches in the train.

eferring particularly to the. embodiment shown in Fig. 1, wherein there is provided means for permitting the calling subscriber, in extending his line over a long train of switches, to release the switch last operated upon discovering that he has sent an improper series of impulses to set such switch, a description will first be given of the opera tion of extending a call through from the calling substation A to the called substation efore proceeding it is to -be observed that while the drawing discloses a train of switches comprising a line finder indicated by its brushes 100, 101, 102; a connector indicated 4by its brushes 103, 104. 105 and two intermediate selectors S and S', there may be inserted any number of selector switches in accordance with the size of the system.

W'lien the subscriber at station A removes his receiver from its hook, the resulting closure of the line 106, 107, causes the finder switch to operate in the veil-known manner to search out and connect with the calling line. This extends the calling lille to a first selector, which for the purpose of the present description is assumed to be inserted in the series between the finder and the selector S shown in detail. The calling subscriber operates his dial 160 to set the first selector on the desired group, and the automatic hunting movement thereupon ensuing extends the line over trunk 108, 109, 110 to an idle second selector, as the switch S. Upon the extension of the connection to switch S, a circuit for the line relay 111 is closed from free pole of battery, through 'the upper winding of relay 111, back contact and upper armature of relay. 112, conductor 109, through the first selector (not shown), finder brush 101, conductor 107, over the loop of substation A, conductor 106, brush 102, through the first selector (not shown), oonductor 110, inner lower armature and back contact of relay 112, lower winding of relay 111 to ground. Relay 111 energizes and closes .a circuit from battery, through the winding of slow relay 113, front contact and armature of relay 111, contact 111 to ground. Relay 113 by attracting its upper armature places a ground on release trunk 108 which serves to prevent the release of the preceding switch as will clearly be shown hereinafter ln connection with the present description of selector S. Relay 113 at its lower armature inserts a break in the circuit of release magnet 115, and also prepares a circuit for the rimar ste in ma net 116.

The call'iyng giibs'iberg now manipulates his dial 160 to transmit a group selecting series of impulses to switch S. At each interruption of the line circuit, relay 111 vibrates its amature and closes the following operating circuit for the magnet 116; grounded contact 114, armature and back contact of relay 111, contact and middle lower armature of relay 112, lower armature and front contact of relay 113, winding of slow relay 117, through the winding of magnet 116 to battery and ground. Relays 113 and 117 being constructed to release their armatures slowly remain operated during the sending of impulses. The magnet 116 responds to the closure of its circuit and operates to advance brush shaft 11S step by step in the primary direction. and finally brings the brushes 119, 120, 121 to rest in operative relation to the group of terminals of trunks leading in the proper direction. The energization of relay 117 closed a circuit from battery, through the winding of relay 122, armature and front contact of relays 117 to ground. Relay 122 attracts its armatures and as soon as the shaft 118 takes its first primary step, a holding circuit is completed as follows for said relay 122: battery, through winding of test relay 122, front contact and inner armature thereof. primary off-normal contact 123. right-hand armature and contact of magnet 124. conductor 125, to ground at the upper armature of relay 113. On the cessation of the line interruptions relay 111 remains energized and after a short period slow relay 117'retracts its armature. A circuit is thereupon closed for the secondary stepping magnet 124 from battery, through the winding of magnet 124, left-hand armature and contact of said magnet, back contact and armature of rela 117, front contact and inner armature o relay 122, contact 123, righthand armature and contact of magnet 124, conductor 125, to ground at the upper armature and contact of relay 113. Magnet 124 energizes to advance brushes 119, 120, 121 onto the first set of .termin-als in the chosen group, and by attracting its left-hand armature opensrits own circuit. The attraction of the right-hand armature of magnet 124 also savers the above traced holding circuit of relay/122. The test brush 119, however, reaches the test terminal of the first set slightly before the armatures of magnet 124 -ture' and contact of relay attracted. If then it be assumed that the first trunk is busy a ground potential will be found by test brush 119 on the testterminal 126, and the following circuit is closed for relay 122 prior to the interruption of its original hol ing circuit: battery, through the winding of relay 122, front contact and inner armature thereof, test brush 119, to the busy grounded terminal 126. Relay 122 therefore remains energized and magnet 124 on retracting its armatures again closes its energizing circuit to are completely -advance brushes 119, 120, 121 step by step over all busy terminals. This operation conded test terminal 126 tinues until an ungroun is found, at which time relay 122 denergi'zes, opening the circuit of magnet 124 to thereby arrest brushes 119, 120, 121 on terminals 126, 127, 128 of a trunk leading to the switch S.

On the retraction of the armatures of relay 122, the following preliminary circuit is completed for relay 112: battery, through the winding of such relay, right-hand armature and contact of magnet 115, back contact and inner armature of relay 122, contact 123, right-hand armature and contact of magnet 124, to ground at the upper arma- 113. Relay 112 on energizing extends trunk conductors 109 and 110 through to switch S', and thereby' completes as follows, a circuit for linerelay 129: battery, through the upper winding of relay 129, back contact an uppermost armature of relay 130, terminal 127, brush 120, front contact and up ermost armature of relay 112, conductor 10. thence over the loop of substation A as described, returning by way of conductor 110, inner lower armature and front contact of relay 112, brush 121, termi-nal 128, inner lower armature and back Contact of relay 130, lower winding of relay 129, to ground. Relay 129 closes a circuit from battery through the winding of slow relay 131, front contact and armature of relay 129, to ground at the closed contact 132.

At the time relay 112 was energized, it opened the circuit of line relay 111, which interrupted the circuit of relay 113. After a suiicient interval has elapsed, relay 113 retracts its armatures and opens the above traced preliminary energizing circuit of relay 112. In the meantime, however, an before this occurs, the rela 131 at switch S has been energized as explained, and establishes the following substltute circuit for relay 112: battery, through the winding of relay 112, right-hand armature and contact of magnet 115, back contact and inner armature of relay 122, brush 119, terminal 126,

contact 133, to ground at the upper armature' 131. The presence of 126 renders the switch busy to other switches. Relay 113 at switch S on releasing opens the ground connection to wire 125. The off-normal contact 134 having been actuated when the switch S took its first primary movement, a ground is maintained on the test wire 10S to prevent release of the preceding switch.

The mechanism is now ready to receive the next set of'directive impulses, and the calling party by manipulating dial 160, causes a corresponding series of interruptions in the above traced circuit of line relay 129. For each retraction of the amature of relay 129, the following circuit is closed `for the primary stepping magnet 135, which operates to advance brushes 136, 137, 138 step by step in the primary movement: grounded contact 132, armature and back contact of relay 129, contact and middle lower armature of relay 130, lower' armature and front contact of relay 131, through the windings ofslow relay 139 and magnet 135 to battery. Relay 139 closes a circuit for relay 140, which in turn locks up over a circuit traceable from battery, through the winding of relay 140, front contact and lower armature thereof, contact 141, closed on the first step of the shaft 149, right-hand armature and contact of secondary magnet 142, to ground at the armature and contact of relay 131. Then the sender 160 restores, the line relay 129 remains permanently energized and after a brief interval slow relay 139 retracts its armature. De'e'nergization of relay 139 establishes a circuit from battery, through the winding of secondary stepping,magnet 142, left-hand armature and contact thereof, back contact and armature of rela 139, front contact and lower armature o relay 140, contact 141, to ground as above traced at the upper armature of relay 131. The magnet 142 operates in a manner similar to that already described in connection with the secondary movement of switch and contact of relay ound on terminal llO S to advance brushes 136, 137, 138 over the selected group, and into engagement with terminals 143, 144, 145 of a trunk leading to an idle connector switch. When test brush 136 reaches the non-grounded terminal 143, the test relay 140 denergizes as hereinbefore described and stops the hunting movement. Relay 140 by retracting Aits armatures closes as follows a circuit for relay 130: battery, through the winding of relay 130, right-hand armature and contact of ma et 146, back contact and lower armature onrelay 140, to ground at the armature and contact of relay 131 over the path previously traced. Relay 130 on energizing extends the connection through to the connector 103, 104, 105, and completes a circuit for the line relay (not shown) at said connector. In the well-known manner the energization of the connector line relay causes the application of a ground "back upon the test terminal 143 at switch S' to provide a new holding circuit for relay 130 prior to the disruption of its original circuit by the denergization of slow relay 131. This circuit for relay 130 is traceable from battery, winding of suchrelay, right-hand armature and contact of ma et 146, back contact and lower armature olielay 140, brush 136, to the rounded terminal 143.

T e calling subscriber now operates his sender 160 to send the last two series of impulses, which control the movement of the connector switch to finally complete the extended connection to the line of the substation B.

lVhen conversation has been finished, either the callin subscriber by replacing his receiver, or t e calling and called subscribers by both replacing their receivers, will cause in the well-known way the release of the connector; and the removal of ground from test terminal 143. The removal of ground from terminal 143 causes the denergization of relay 130, which retracts its armatures and closes the following circuit for release magnet 146: battery, through the winding of said ma et, primary oiinorlnal contact 147, 'bac contact and lower armature of relay 131, middle lower armature and contact of relay 130, back Contact and armature of relay 129, to grounded contact 132. Magnet 146 energizes to release switch S to normal position. As soon as the switch is completely restored, contact 148 opens and removes ground from test terminal 126, which results in the restoration of the switch S in a manner similar to that just described for switch S. All switches preceding selector S are likewise restored to normal.

The case will next be assumed in which the calling party at A in building up a connection to the called line inadvertently sends out a false set of impulses to set a switch such as selector S in relation to some trunk group other than the desired group. As soon as the switch S has completed its secondary movement and has chosen an idle trunk in the false group, which for the purpose of the present discussion will be considered as a trunk leading to selector S', a circuit for the line relay 129 is closed. This circuit has `already been traced and need not be again described. The calling subscriber nowA transmits a special series of eleven impulses, the sender 160 being constructed to accomplish this pu ose, to the switch S', resulting in the brus shaft 149 being advanced eleven primary steps. On the shaft 149 taking its eleventh step, a special contact 133 in the release trunk is opened. This removes both the ground at primary i olf-normal contact 148 and the ground at the primary off-normal contact 134 from test terminal 126. The previously traced circuit for relay 112 is therefore opened and said relay denergizes. Upon the two inner armatures of relay 112 reaching their back contacts, relay 111 is a ain energized since the line 106, 107 is close at this time. Relay 111 attracts its armature to lace a break point in the above descri ed circuit of release magnet 115, and also causes the energization of relay 113. However, during the retraction of the lowermost armature of relay 112, the contact 114 is so constructed as to maintain a momentary engagement therewith after having made connection with its grounded contact 150. This results in a momentary ground being placed on conductor 151, which causes the energization of magnet 115. Magnet 115 locks up over olf-normal contact 1'52, and restores selector S to normal. A form of relay contact which closes a circuit momentarily on the back stroke of `its armature in the manner described in connection with the lowermost armature of relay 112 and lowermost armature of relay 110 130 is shown and described in the copending application of Clausen, Serial No. 208,844, filed December 26, 1917. On reaching its fully restored position, shaft 118 opens contact 134, but relay 113 being energized at 115 this time maintains a ground on release trunk 108, and hence the preceding switches in the train are left undisturbed. As soon as the switch S removes its brushes 120 and 121 from terminals 127 and 128, the circuit of 120 line relay 129 is opened resulting in the closure of the circuit of release magnet 146 in the manner already described. Switch S thereupon restores to normal. The calling subscriber may proceed with the dialing op- 126 eration at the point where the false digit was sent.

A description will now be given of the embodiment of the invention shown in Fig. 2. This modification of the invention is ob- 130 viously well adapted to use in private branch exchanges where it is often desirable for an outside calling subscriber to obtain several successive connections with di'erent subscribers in the same exchange. There are shown the detailed circuits of a connector C and a selector S2 which may well be considered as located in a private branch exchange, and while there is indicated only a iinder switch by its brushes 200, 201, 202, and a selector by its brushes 203, 204, 205, such as may be situated in a central office, it is to be understood that the train ofl switches preceding the selector S2 and connector C may comprise any suitable num ber of switches.

Upon the removal of the receiver from its hook at the substation A', the line circuit 206, 207 is closed to initiate the operation of the inder switch. The line is thereby extended to an idle selector switch having brushes 203, 204, 205, and the calling subscriber by manipulating his sender 208 sets said selector on the terminals of a trunk leading to an idle selector in the desired private branch exchange, such as selector S2. Upon the extension of the connection to switch S2, a circuit is established for line relay 209 from battery, through the upper winding of such relay, backcontact and uppermost armature of relay 210, brushes 204 and 201, conductor 207, over the loop of substation A. conductor 206, brushes 202 and 205, inner lower armature and back contact of relay 210, lower winding of relay.

209, to ground. Relay 209 by ener zing closes a circuit from battery throug the winding of slow relay 211, front contact and lower. armature of relay 209, to ground. Relay 211 operates and at its upper armature places a ground on the test wire 212, whereby the preceding switches are prevented from releasing. This ground is ap plied over a circuit from the inner righthand armature and back contact of relay 213, contact and upper armature of relay 211. closed contact 214, to test wire 212. Relay 211 at its lower armature places a break in the circuit of release magnet 215, and also prepares an operating circuit for the primary stepping magnet 216 When the calling party operates his sender 208 to produce a series of line interruptions in accordance with the second digit of the called number, the line relay 209 vibrates its armatures in response to such interruptions, and for each retraction of the lower armature thereof, the following circuit is closed for the primary stepping ma net 210: lower grounded armature and bac contact of relay 209, contact and lowermost armature of nelay 210, lower armature and front contact of relay 211, winding of relay 217, through the winding of the magnet 216 to battery and ground. Magnet 216 operates to step the brushes 218, 219, 220, 221 in the primary movement into operative relation with the desired group of trunks. The slow relay 217 energizes in the circuit just traced and closes a circuit from battery, through the winding of test relay 222, armature and front contact of relay 217 to ground. Test relay 222 attracts its armature and a holding circuit therefore is closed as follows: battery, through the winding of said relay 222, front contact and armature thereof, primary off.- normal contact 223, contact and right-hand armature of the secondary stepping magnet 224, upper armature and contact of relay 211, back contact and inner right-hand armature of relay 213 to ground.

At the end of the primary series the line relay retains its armatures closed and after a brief interval, slow relay 217 denergizes and a circuit is thereupon established for the secondary stepping magnet 224. This circuit may be traced from battery, through the winding of said magnet, left-hand armature and Contact thereof, back contact and armature of relay 217, front contact and armature of relay 222, contact 223, contact and righthand armature of magnet 224, upper armature and contact of relay 211 to ground at the back contact and inner right-hand armature of relay 213. Magnet 224 energizes to advance the brushes 218, 219, 220 and 221 onto the first set of terminals of the selected grou and by attracting its left-hand armature interrupts its own circuit. Said magnet by attracting its right-hand armature also opens the previously traced circuit for the test relay 222. The right-hand armature of magnet 224 is adjusted, however, so as not to break connection with its coperatin contact until slightly after the test brus 221 is in engagement with the test terminal 225. In the event then that the first trunk in the group is busy, a ground will be found upon the` terminal 225 and the following substitute circuit is established for test relay 110 222 in the place of its original circuit, which is now open as described by the energization of the stepping magnet 224: battery, through the winding of relay 222, front contact and armature thereof, test brush 221, to the 1115 grounded terminal 225. Relay 222, therefore, remains energized and magnet 224 upon retracting its armatures closes its energizing circuit again and the brushes are advanced a second step forward. This operation is 120 maintained until an idle trunk is encountered upon the test terminal 225 on which no ground is present. At this time relay 222 denergizes, which results in bringing the switch to rest on the terminals of the idle 125 trunk.

On retracting its armature.` relay 222 closes the following preliminary circuit for relay 210: free pole of battery. through the winding of relay 210, back contact and armature 130 of relay 222, contact 223, contact and righthand armature of magnet 224, upper armature and contact of relay 211, to ground at the back contact and inner right-hand armature of relay 213. Relay 210 by attracting its armatures extends the calling line through to the brushes 219 and 220 and thence to the connector `switch C. This results in the establishment of the following circuit for the calling line relay 226: free pole of battery, left-hand winding of said relay, contact 227, terminal 228, brush 219, front contact and uppermost armature of relay 210, brushes 204 and 201, conductor 207, over the loop of the calling station A', conductor 20G, brushes 202 and 205, inner lower armature and front contact of relay 210, brush 220, terminal 229, Contact 230, through the right-hand winding of relay 226 to ground. Relay 226 closes a circuit for the slow relay 231 from battery, through winding of said relay, front contact and' lefthand armature of relay 226 to ground. Relay 231 at its left-hand armature applies a ground potential tothe test terminal 225 to render this connector busy to other selector switches. When the relay 210 energizes, it sevcrs the hereinbefore described circuit of relay 209, which in denergizing opens the circuit of reiay 211, which in turn by retracting its armatures opens the above traced preliminary circuit for relay 210. Relay 211, however, being slow to release, does not open the said preliminary energizing circuit of relay 210 until after relay 231 has been energized, as described, to establish a substitute circuit for relay 210 as follows: battery, through the winding of relay 210, back contact and armature of rela 222, test brush 221, terminal 225 to groun at the left-hand armature and contact of relay 231. '1 he ground on the terminal 225 is also applied back to the test wire 212 to revent the releasing of the preceding switc es after slow relay 211 dener izes to remove therefrom the `ground at the inner right-hand armature of relay 213, which has been held applied to the said test wire 212 during the operating period of the selector S2. The path for the application of this new holding ground is traceable from test terminal 225, brush 221, contact 223, contact and right-hand armature of magnet 224, contact 214 to the test wire 212.

The calling subscriber again manipulates the sender 208 to transmit the tens digits and at each interruption of the line circuit, the line relay 226 retiacts its armatures. At the first ('lenergization of relay 226, the following circuit is closed for operating the primary stepping magnet 232: left-hand armature and back contact of relay 226, righthand armature and front contact of relay 231, winding of slow relay 233, through the winding of the magnet 232,

side-switch arm 234, position 1, to battery. Magnet 232 energizes and advancesl the brushes 235, 236 and 237 one step in the primary or group selecting direction. For each succeeding retraction of the armature of relay 226, magnet 232 operates to advance said brushes step by step into operative relation with the desired group of line terminals. During the operation of the primary stepping magnet, slow relay 233 remains energized and establishes a circuit from battery, through the winding of escape magnet 238, contact 239, armature of relay 233 to ground. At the end of the rimary series of impulses, relay 233 denergizes and opens the circuit of escape magnet 238, which in turn releases the side switch into its second position.

Upon the transmission of the final or units series of impulses, relay 226 vibrates its armatures as before, and at each retraction thereof the following operating circuit is closed for the secondary stepping magnet 240: grounded armature and back contact of relay 226, right-hand armature and front contact of relay 231, winding of slow relay 233, outer left-hand armature and contact of relay 241, through the winding of the magnet 240, side-switch arm 234, position 2, to battery. Magnet 240 operates to advance the brushes 235, 236 and 237, step by step over the selected group of terminals in engagement with the terminals 242, 243 and 244 of the called line. Assuming the called line to be busy at this time, ground potential will be found upon the test terminal 244, having been applied thereto either from a finder or selector switch in case the line is busy as a calling line, or from a side-switch arm corresponding to arm 245 at some other connector in the event the line is busy as a `called line. In either case the slow relay 233 in de'c'nergizing at the end of the series of impulses permits the contact 239 to engage its coperating contact before the armature of said relay breaks engagement with the said Contact 239. This establishes a substitute circuit as follows for preventingI the escape magnet from passing the side switch into position 3: battery, through the winding of escape magnet 238, contact 239, through the winding of relay 241, contact 246, side-switch arm 245, position 2, brush 237 to the grounded test terminal 244. Relay 241 energizes in this circuit and a itsl right-hand armature and inake-before-break contact 246 prepares a new circuit for i self in series with the escape magnet 238 which may be traced from battery, through the winding of magnet 238, Contact 239, winding of relay 241, contact 2-16 and right-hand armature of said relay to ground at the primary of-iioi'nial contact 247. Relay 241 also closes a circuit from the grounded secondary winding of busy tone machine 218, inner well-known manner back to the callin left-hand armature and contact of relay 241 to conductor 249. Current from the busy tone machine may be transmitted in titre su station A to inform the subscriber t ereat that the called line is engaged.

The subscriber at A upon receiving this notification replaces his receiver on the hook,

which results in the denergization of the line relay 226. After a brief interval the slow relay 231 retracts its armatures and Vcloses the following circuit for the connector release magnet 250: from battery, through the Winding of said magnet, primary olfnormal contact 251, back contact and righthand armature of relay 231, back contact and left-hand armature of relay 226 to ground. Ma net 250 operates in response to the closin o this circuit to restore the connector switch C to its normal position.

The retraction of the left-hand armature of relay 231 also removes ground from the test terminal 225 to o en the above traced circuit of relay 210 w ich denergizes and prepares the followin circuit for the release magnet 215 of the se ector switch S2: battery, throu h the winding of magnet 215, primar o -normal contact 251, back contact an lower armature of relay 211, lowermost armature and contact of relay 210, back contact and lower armature of relay 209 to ground. selector switch S2 to normal. Ground'is, at the same time, removed from the test conduotor 212, with the result that the recedin switches` in the train are restoredpn the we l-known manner. v

In case, however, the called line is idle at the time the connector C makes the test thereof, no ground will be found on the terminal 244. Therefore, as the relay 233 deenergizes after .the cessation of the secondary series of impulses, the circuit of the escape magnet 238 is interrupted. Escape magnet 238 thereupon denergizes andY releases the side switch into its third position. In this osition of the side-switch arm 245, a groun potential is placed upon the terminal 244 to render the called line busy, and the following circuit is also closed for relay 253: battery, winding of said relay, contact and armature of magnet 238, side-switch arm 245 to ground. Relay 253 by attracting its armatures closes conductors 254 and 255 through to the brushes 235 and 236 respectively. Side-switch arm 234 on reaching its third position closes a circuit for the ringing relay 252. This circuit may be followed from battery, side-switch arm 234, inner right-hand armature and contact of ringing cutoi relay 256, through the winding of relay 252, interruptor 257 to ground. Relay 252 is intermittently actuated by the interruptor 257 to apply ringing current to the called line.

Magnet 215 thereupon restores- The ringing circuit may be traced from the ringing source 253, front contact and lower armature of relay 252, conductor 255, lower armatureand Contact of relay 253, brush 236, terminal 243, over the called line through the bell at substation B', returning by terminal 242, brush 235, contact and upper armature of relay 253, conductor 254, upperarmature and front contact of relay 252 to ground. When the called party responds by removing his receiver from the switch hook, during the' period that the ringing relay 252 is denergized, the following circuit is established for the energization of the called line rela f 259: battery left-hand winding of said re ay, conductor 249, back contact andlower armature of relay 252, lower armature and contact of relay 253, brush 236, terminal 243, over the loop at substation B', terminal 242, brush 235, contact and upper armature of relay 253, conductor 254, upper armature and back contact of relay 252, through the right-hand winding of relay 259 to ground. Relay 259 by attracting its right-hand armature closes a circuit from battery, side-switch arm 234, position 3, through winding of relay 256, conductor 260, front contact and right-hand armature of relay 259, to ground at the oil'- normal contact 247. Relay 256 energizes and interrupts the above traced circuit for the ringing relay 252, thereby bringing to a close the ringin operation. Conversation may now take p ace, talking current being transmitted to the callin line through" the Windin s of rela 226 and to the called line throng the win ings of relay 259. At the termination of conversation, the calling party, by replacing his receiverV on the switch-hook, causes the restoration of the 106 switches in the manner already described Assuming that after havin completed his conversation with the subscri r at the substation B,the calling subscriber at A desres to converse with another party in the 110 same exchange. He may do so Without necessitating the restoration of the complete train of switches involved in the establishment of the original connection. To accomplish this, it is only required that the calling subscriber manipulate his dial 208 to transmit a special series of eleven impulses to the connector C. For each one of these line interruptions, the line relay 226 is intermit- Vtently denergized and energized. The righthand armature of-said relay is so constructed as to coperate with its make-before-ibreak contact 261 in such a manner that battery potential is applied t0 the conductor 262 once during retraction and again during attraction of said armature. For eleven impulses sont to the relay 226, the result is that the following circuit is momentarily closed twenty-two timos in succession: battery, xnakc-bcforc-break contactk 261, right-hand amature of relay 226, conductor 262, through the winding of solenoid 263, sideswitch arm 264 to ground. Solenoid 263 1s made slow to attract its lun er 265 such that it is necessary to sen at east twentytwo consecutive impulses to said solenold before'its plunger is attracted to its full forward position. Plunger 265, therefore, operates to close the contact 266, which esta lishes a circuit from battery, through .the winding of relay 213, brush 218, terminal 267, Contact 266 side-switch arm 264, position 3, to ground. Relay 213 energizes and locks up over a circuit from battery, through the Winding of relay 213, contact and outer right-hand armature of said relay, to ground at the primary olf-normal Contact 268. Relay 213 closes a circuit for the release magnet 215 from battery, through the winding of said magnet, contact 251, conductor 269 to ground at the inner right-hand armature and front contact of relay 213. Magnet 215 is thereby energized torestore thefselector switch S2 to its normal position. The test brush 221, on leaving the terminal 225 interrupts the previously traced circuit for the application of ground potential to the test wire 212 at selector S2, but relay 213 at its left-hand armature and make-before-break contact 214 has already applied a substitute ground to the wire 212, which thereby prevents the release of any of the switches preceding the selector S2. The test ibrush 221 on leaving the terminal 225 furthermore causes the opening of the circuit for relay 210, which therefore denergizes. Relay 210 on retracting its armatures prepares the above traced circuit for the line rela 209 in series with the callin line since the atter is closed at this time. lay 209 energizes before the switch has hadA time to fully restore to its normal position, and at its upper armature applies ground'to the test wire 212 for a' `pur ose which will presently be described. s soon as the switch `S2 rea-ches its normal position, contact 268 is opened and relay 213 thereby retracts its left-hand armature to remove ground from the test wire 212. Relay 209 as above described has, however, in the meantime, applied a substitute ground to said test wire whlch prevents the release of the preceding switches, until relay' 213 has `had suicient time to retract its inner right-hand armature and apply a holding round to the test conductor 212 over the ollowin circuit: inner right-hand armature and bac Contact of relay 213, front contact and upper armature of relay 211, contact 214 to thewire 212...

As soon as the brushes 219 and 220 break engagement with yterminals 228 and 229 upon the restoration of switch S, the circuit of line relay 226 at the connector switch C is opened, resulting in the release of said connector in the manner already described.

automatic switches for interconnecting said 1 lines, means controlled by the operation ofy the calling subscribers sender for setting the automatic switches, means for releasing all of the set switches, and means responsive to a definite operation only of the calling subscribers sender for releasing only a portion of the set switches.

2. In a telephone system, a calling and a called line, an' lmpulse sender associated with the calling line, selective switches for interconnecting said lines, impulse responsive means operated by impulses sent from said sender for setting the automatic switches, means under the control of the calling subscriber for releasing all of the set switches, and means responsive to not less than a definite number of impulses sent' by said sender for releasing a portion only of the set switches. v

3. In a telephone system, telephone lines, a train of automatic switches for interconnecting said lines, means for setting said switches, and means effective after any switch in the train has been set to cause the release thereof without releasing theremaining set switches.

In a telephone system, a plurality of lines, a train of automatic switches for establishing a connection between any two of said lines, means for setting said switches, and means under the control of one of said lines for releasing any set switch in Said train without releasing the remaining set switches in said train.

5. In a telephone system, a calling and a called line, a train of automatic switches for interconnecting said lines, means for setting said switches, and means under the control of the calling subscriber for releasing any set switch in said train without releasing the remaining set switches.

6. In a telephone system, telephone lines, a train of automatic switches for interconnecting said lines` means for settings-ny number of the switches in said train, means for operatin the switch next succeeding the last set switc to release said last set switch without releasing the preceding set switches in sai train.

7. In a telephone system, a calling and a called line, a series of automatic switches for, interconnecting said lines, means under the control of the calling line for setting successively any number of the switches in said series, and means under the control of the calling line for operating one of the switches succeeding the last set switch in the series for releasing said last set switch.

8. In a telephone system, telephone lines, a series of automatic switches each having a plurality of separate movements for interconnecting said lines, means for setting any number of said switches, and means for operating in its primary movement one of the switches succeeding the last set switch for releasing said last set switch.

9. In a telephone system, a calling and a called line, a train of automatic switches for interconnecting said lines, means for setting the successive switches constituting any portion of said train of switches, means controlled by the calling line for releasing all of the set switches, and means controlled by the calling line for releasing only the last set switch.

10. In a telephone system, a calling and a called line, a series of impulse operated selective switches each having a primary and a secondary movement for interconnecting said lines, impulse sending means associated with the calling line for setting any number of the switches of said series of switches, and means responsive to said sending means for advancing to a definite position in its rimary movement the switch next succeed- 1n the switchlast set in said train, whereby said last set switch is restored to normal withoutrestoring the remaining set switches in the series.

In witness whereof, I hereunto` subscribe my name this 21st dgry of Ma A. D., 1918.

HE RY P LAUSEN. 

